Optical cuvettes are containers for holding liquid samples during spectrophotometric measurements. As such, they must be at least partially transparent to the relevant wavelengths of light and have well-defined optical path lengths. In some cases, the cuvettes are designed to facilitate high-throughput applications with specific instruments. When used for making measurements on biological samples, they should allow for accurate measurements on small sample volumes. Fluids such as blood require particularly small optical path lengths to prevent measurement contamination resulting from light scattering and absorption by cellular components.
U.S. Pat. No. 5,430,542, issued to Shepherd, discloses a disposable optical cuvette used for holding whole blood during spectrophotometric measurements. The cuvette is formed from two optically transparent liquid-impermeable plastic sheets sandwiching a third “sticky” sheet that has a cutout defining an optical chamber. Inlet and vent ports are also formed in the sticky sheet. A sample to be analyzed is inserted through the inlet port, and the thickness of the middle layer defines the optical path length. One drawback of these cuvettes is that while a large number of them can be manufactured simultaneously, the individual cuvettes are separated for subsequent use, so that only one sample can be analyzed at a time. Separating the cuvettes is necessary because of the placement of the inlet and vent ports in the middle layer. The cuvette is therefore not suitable for rapid and automated measurements on a large number of samples.
An additional problem with these and other cuvettes is that the optical properties of the material used to form the cuvette may interfere with the measurements being performed. For example, when fluorescence measurements are acquired, background fluorescence of the material must be subtracted from the total measurements to obtain the true sample fluorescence.
There is a need, therefore, for a cuvette useful for automated, high-throughput spectrophotometric measurements on small volumes of biological fluid. There is also a need for a cuvette that interferes minimally with the measurements being performed.